A vehicle grille is typically located at a front end of a vehicle, and can be configured to provide an opening through which intake air is received from outside of the vehicle, such as a grille opening or bumper opening. Such intake air may then be directed to an engine compartment of the vehicle to assist the vehicle's cooling system in cooling the engine, transmission, and other such components of the engine compartment. Such air flow via the grille may add aerodynamic drag when the vehicle is in motion. Accordingly, grilles may include grille shutters to block such air flow, thus reducing aerodynamic drag and improving fuel economy. Closed grille shutters may also provide a faster powertrain warm-up which may improve fuel economy since there is less friction, and may improve the performance of the passenger compartment heater. However, closed grille shutters also reduce the air flow through the radiator and other components for cooling purposes. As a result, engine temperatures such as engine coolant temperature (ECT) may increase. Thus, grille shutter operation may include increasing or decreasing the quantity of the opening of the grille shutters based on engine cooling demands and vehicle driving conditions.
One example approach for adjusting grille shutters is shown by Kerns et al. in U.S. Pat. No. 8,311,708. Therein, vehicle grille shutters are adjusted in response to engine temperature and a non-driven vehicle condition. For example, when engine temperature is above a threshold temperature, the grille shutters may be opened.
However, the inventors herein have recognized potential issues with such systems. As one example, the grille shutters may open in response to ECT increasing above a first threshold temperature. However, the ECT may continue to overshoot past the first threshold until the ECT begins to cool down due to the opened grille shutters. Then the grille shutters close in response to ECT decreasing below the first threshold or a second threshold, lower than the first. However, the ECT may continue to undershoot past the second threshold until the ECT begins to heat up again due to the closed grille shutters. Controlling the ECT in response to one or more set thresholds, based on a current ECT, may result in degraded aerodynamics and fuel economy. At the same time, not opening the grille shutters soon enough (at the appropriate threshold) or by a large enough amount to compensate for an increasing ECT may cause engine temperatures to continue to increase, thereby degrading engine performance.
In one example, the issues described above may be addressed by a method for adjusting active grille shutters positioned at a front end of a vehicle into a position, such as a final position, at or between a first position having a smaller amount of opening and a second position having a larger amount of opening based on a rate of change of an engine coolant temperature and a difference in aerodynamic drag between the first and second positions. In this way, by continuously adjusting the grille shutter opening between the first and second position based on the thermal cooling requirements of the engine and the estimated aerodynamic drag, overheating or overcooling of the engine may be reduced, while also reducing average aerodynamic drag, and as such may increase fuel economy.
As one example, adjusting the active grille shutters into the final position includes adjusting the active grille shutters closer to the first position than second position as the difference in aerodynamic drag increases and adjusting the active grille shutters closer to the second position than the first position as the difference in the aerodynamic drag decreases. Thus, by opening the grille shutter by a smaller amount when the aerodynamic drag increases, the ECT may slowly increase while keeping aerodynamic losses at a lower level, thus increasing fuel economy. Additionally, by opening the grille shutter by a larger amount when the aerodynamic losses are smaller, the engine may be maintained at lower temperatures and hence ECT may be maintained at a lower level, thereby increasing engine oil life, and in some operating conditions increasing engine efficiency.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.